Plastic extrusion machine

ABSTRACT

Apparatus for extruding plastic materials which includes a housing having a stator, a rotor in the form of a plate arranged in face-to-face relation with the stator to define a gap between the rotor and the stator, an extrusion opening axially through the rotor, means to rotate the rotor relative to the stator, an annular channel defined by the housing and means to sweep the volume of the annular channel whereby plastic is displaced toward the extrusion opening.

United States Patent Inventors Appl. No. Filed Patented Assignee PLASTICEXTRUSION MACHINE 12 Claims, 6 Drawing Figs.

US. Cl .l 18/12 C, 18/12 SE Int. Cl 1329i 3/00- Field of Search 18/12 C,12

DR, 128E.

References Cited UNITED STATES PATENTS 3,046,603 7/1962 Maxwell 18/12(C) X 3,153,686 10/1964 Adams l8/12(C)X 3,308,505 3/1967 Bearer et al.18/12 C UX Primary Examiner-H. A. Kilby, Jr. Att0rneyMcDougall, Hersh,Scott & Ladd ABSTRACT: Apparatus for extruding plastic materials whichincludes a housing having a stator, a rotor'in the form of a platearranged in face-to-face relation with the stator to define a gapbetween the rotor and the stator, an extrusion opening axially throughthe rotor, means to rotate the rotor relative to the stator, an annularchannel defined by the housing and means to sweep the volume of theannular channel whereby plastic is displaced toward the extrusionopening.

PATENTEDSEP 7|97I 3,602,943

sum 2 or 4 FIG. 3

'FIG.4

PATENTEU SEP 7 '9?! sum u or 4 FIG. 6

, means to feed the material to be extruded to the extrusion orifice.

To avoid certain disadvantages inherent in conventional single-screwextruders, apparatus which makes use of a normal force effect sometimesreferred to as the Weissenberg effect has been developed. This effect,which is used for the extrusion of thermoplastic materials, is developedby the use of an apparatus having at least two parallel surfaces with aspace therebetween into which the thermoplastic material is introduced.One of the surfaces is held stationary while the other is rotatedrelative thereto about an axis perpendicular to the surfaces, with anopening through the fixed surface through which the plastic materialextrudes. In U.S.Pat. No. 3,364,522, issued Jan. 23, 1968, and entitledPlastic Extrusion Machine, description is made of a device of the typedescribed which is adapted for the extrusion of thermally unstablepolymers and particularly unplasticized polyvinyl chloride. As describedin the aforementioned patent, the device is formed with a cavity that iseccentric to the rotating plate or rotor and which has a plurality ofcurvilinear deflector blades extending therein from one or the other orboth of the surfaces to enhance homogenization of the thermoplasticmaterial as well as its rapid displacement, while the plastic state,toward the extrusion opening whereby to" void thermal degradation of theresin. In U.S. Pat. No. 3,41 1,180, granted Nov. 19,1968, and entitledPlastic Extrus ion Machine,38 description is made of an improvement inthe apparatus of the type described in which chamfers are provided inthe peripheral portions of the rotor and the stationary disc plate orstator, with the chamfered portions having an interfitting relationshipor nesting relationship therebetween to enable relative rotationalmovement without friction but with minimum clearance, This improvementpermits use of the apparatus for extrusion of unplasticized polyvinylchloride through die openings of small cross section, as in the production of filaments and the like.

. In copending application Ser. No. 759,087, filed Sept. 1 l, 1968, andentitled Improvement in Extruders with Rotating Plate, 38 description ismade of an extruder having a rotating plate in which at least one of thefaces of the plates is formed with grooves extending tangentially to acircle concentric with the axis of the plate. This improvement allowsthe use of the apparatus for extrusion of polymers containing lubricantwherein it is possible to extrude at higher temperatures and/or toobtain better homogenization and/or to improve the flow and ease ofshaping of the material to the desired product.

In copending application Ser. No. 764,860, filed Oct. 3, 1968, andentitled Improvement in Rotating Plate Type Extruders, description ismade of a rotating-plate-type extruder in which the surface in thecentral axial portion of at least one of the plates is recessed toincrease the width of the gap between the plates in communication withthe extrusion openmg.

Difficulties have been experienced in the use of such apparatus for theextrusion of some polymers, especially polyvinyl chloride withoutexperiencing a perceptible amount of degradation and/or choking of theapparatus. The rapid gelling of the resin to be extruded is often acause of afeed disturbance in that the rotating plate does not empty thefeed hopper at a sufficient rate, with the result that the extruderbecomes clogged o choked.

It is an object of the present invention to provide an extruder withimproved feeding means which overcomes. the foregoing deficiencies.

It is another object of the present invention to provide means to insurethe rapid and uniform progression of the material to be extrudedtoward'extruder orifice.

These and other objects and advantages of the invention will hereinafterappear and for purposes of illustration, but not of limitation,embodiments of the invention are shown in the accompanying drawings inwhich:

FIG. 1 is a view in axial section of one embodiment of the presentinvention.

FIG. 2 is a top view of the device shown in FIG. 1 after the rotorhousing has been removed;

FIGS. 3 and 4 are top views of FIG. 1 except that they show alternativearrangements for rotor blades;

FIG. 5 is a view in axial section of another embodiment of the presentinvention; and,

FIG. 6 is a sectional view of the embodiment shown in FIG. 5 taken in aplane perpendicular to the axis of the rotating plate. I

The improvement of the present invention resides in providing anextruder which has an annular channel circumscribing the space or gapbetween the plates and which is concentric with and communicates withthe space between the plates, and means fixed on the inner surface ofthe rotating plate to sweep the volume of the annular channel.

In accordance with one embodiment of the present invention, the annularchannel lies in substantially the same plane as the fixed plate orstator and is bounded at its bottom by the plane of the stator The outersidewall of the channel is a cylindrical surface defined by the housingsurrounding the rotor, and the inner side is bounded by the spacebetween the plates. The upper portion of the annular channel is boundedeither by the plane of the interior surface of the rotor or by ahelicoid, the maximum height of which is on one side of the hopperadjacent thereto and decreases in the direction of rotation of therotating plate to a minimum height equal to the distance between theplates on the other side of the hopper.

The width of the annular channel along an extended radius of the rotoris preferably n greater than the radius of the rotor, and generally istwo to five times the distance between the plates, The maximumheight ofthe annular channel along the axis of the rotor generally depends uponthe ratio between the apparent density of the material to be extruded atthe inlet to the apparatus and the apparent density after extrusion. Itis generally preferred that the maximum height be between one and threetimes the distance between the plates.

Another feature of the present invention relates to the lower portion ofthe hopper which supplies resin to be extruded to the annular. channel.The lower portion of the hopper, the width of which is approximately thesame as the width of the annular channel, is closed by a horizontalplate, but is provided with the side and opening or window, preferablyin a plane passing through the rotor axis to permit the material to betreated to flow in the direction of rotation of the rotating disc. Inembodiments in which the annular channel is bounded at its top portionby a helicoid and thus has a decreasing height, it is generallypreferred to set the height of the window at a, level corresponding tothe difference between the maximum and minimum heights of the channel.In embodiments where the channel has a constant vertical height, thereis generally provided a recess in the channel to permit flow of thematerial to be extruded from the hopper into the annular channel. Thelower portion of the window formed at the bottom of the hopper ispreferably in the plane of the internal surface of the rotation plate.

Another feature of the present invention resides in the use of aplurality of deflecting blades which are movable through the annular.channel about at least one fixed point or crown. It is generallypreferred that the blades be integral with the rotor. I r

The blades are preferably fixed to the internal surface of the rotatingplate and can be integral therewith, and also can be connected to eachother to form one integral blade. The blades andthe internal surface ofthe stator have a profile such that the material to be extruded isdisplaced to the space between the plates. When rotated, the bladesscrape the material on the bottom of the annular channel andsimultaneously exert a centripetal forceon the material displacing ittoward the extrusion orifice, thereby continuously clearing the feedhopper. The rotating plate may be provided with any number of blades,although it is preferred to embody a rotor having three to six blades.It has been found that it is possible to increase by 30 percent thefeed-flow capacity of the extruder by increasing the number of bladesfrom three to six.

The vertical height of the annular channel should be sufficient topermit the passage of the blades of each of the crowns mounted on therotary plate. When there is more than one crown on the rotary plate, itis generally preferred that the crowns be spaced at a distance equal tothe thickness of the fixed crown located between them so that there willbe no substantial overlap in the volume swept by the blades of eachcrown. The vertical height of the annular channel adjacent the spacebetween the plates may be reduced if desired to a dimensioncorresponding to that of the space between the plates.

Referring now to the drawing for a description of a discplate extruderembodying the features of the invention, there is shown in FIG. 1, aplate 1 or rotor adapted to be rotated in a horizontal plane about avertical axis and which has conventional heating means, such as hollowedchannels or passages 2 for circulation of a thermostatically controlledheat-transfer fluid, on its outer surface. Positioned in a face-to-faceparallel relation to rotor l is a fixed plate or stator 3 which formsthe lower portion of the extruder and which is similarly provided withconventional heating means 4. The stator has an orifice 5 at its centerthrough which a polymer may be extruded. Rotor 1 is preferably mountedabove stator 3 such that the axis of the rotor is coincident to thecenter of opening 5 and such that the inner horizontal surfaces define aspace or gap 6 therebetween. Rotor 1 is mounted to be rotatable relativeto stator by conventional means (not shown) attached to shaft 13. Theinterior surface of the rotor may be provided with various reliefelements, such as grooves as disclosed in copending application Ser. No.759,087, and/o an axial protuberance or crown 7 depicted in the drawing.

Circumscribing rotor 1 and gap 6 is an annular housing or ferrule 8 inwhich the rotor is adapted to be rotated with a minimum clearance suchthat the rotor will not generate substantial friction when the device isempty. Ferrule 8 is provided with an opening into which a feed hopper 9or the like may be positioned. Feed hopper 9 is closed at its bottom,but is provided with a small window 11 through which the material to beextruded can flow from the hopper to the annular channel in thedirection of rotation of the rotor.

Ferrule 8 also defines an annular channel 10 which is located around thecircumference of gap 6 and communicates therewith. On the inner surfaceof rotor 1, there is provided at least one blade 12 which protrudes intoannular channel 10. Adjacent and on one side of hopper 9, annularchannel 10 has a maximum vertical height corresponding to the sum of thevertical distance between rotor 1 and stator 3 and the vertical heightof the hopper window. The height of annular channel 10 diametricallyopposite the hopper (shown on the right in FIG. 1) falls between themaximum height and the minimum height, which corresponds to the heightof the space between the plates on the other side of the rotor.

In accordance with this embodiment, as rotor 1 having blade 12 fixedthereon is rotated, blade 12 scrapes the material on the inter surfaceof stator 3 and displaces it toward the extruder orifice 5. As blade 12rotates from the window of the hopper, it approaches the inner surfaceof rotor l to thereby continuously empty the hopper, and displace placethe material toward orifice 5.

It will be understood that the height of the annular channel 10 may be aconstant. In this embodiment, the distance between the bottom of theblade and the inner surface of rotor 1 remains constant.

FIG. 2 is a top view of the apparatus shown in FIG. l. after housing 8has been removed. It will be seen that a plurality of blades 12a, 12b,and 12c are mounted on rotor l and extend into annular channel 10.

FIG. 3 depicts the internal surface of rotor 1 as viewed from inside theextruder. It is generally preferred that blades 12a, 12b, and 12c have afin-shaped arcuate configuration as depicted in this figure so that theywill impart a centripetal component to the forces acting upon thematerial to be extruded to cause it to move toward the die orifice. Itwill also be seen that the blades are mounted on a cylindricalprojection or crown 14 which is an integral part of rotor 1.

FIG. 4 is a variation of the embodiment depicted in FIG. 3, wherein atleast one single cylindrical rod 12 affixed to crown 14 which isintegral with rotor 1 and is used in lieu of the finshaped blades.

It will be understood that various modifications may be applied to theapparatus from the scope of the invention. For example, it is possibleto use blades of other configurations which similarly exert acentripetal force upon the material to be extruded. It is likewisepossible to replace feed hopper 9 by a plurality of hoppers or by asingle annular hopper communicating with annular channel 10 by severalopenings An extruder of the type described above may also be adapted foruse with a horizontal axis by positioning the feed hopper on the statorrather than on the housing. In such an extruder one of the faces of theannular channel is preferably coplanar with the inner surface of therotor, and the other helicoidal face is hollowed out of the face of thestator.

Another embodiment of the present invention is depicted in FIG. 5wherein the extruder is shown as having a horizontal axis. There isprovided a rotor 101 having heating means 108, such as passages, for thecirculation of a thermostatically controlled heat-transfer fluid andhaving cavities around its circumference for mounting a plurality ofblades 102, each of which is comprised of two blade elements 103 and abase 104 adapted to fit the cavity.

A stator 105, also having heating means 109, is positioned in aface-to-face parallel relation with rotor 101 so as to define anairspace or gap 111 between the plates. Rotor 101 is adapted to berotated relative to stator 105 by conventional means such as a gearboxand motor (not shown in the drawing) The stator is provided with opening112 at its center through which material may be extruded. About theperiphery of the inner surface of the rotor and communicating with space111, there is an annular channel which is defined by the surfaces of ahousing or support 106 an fixed crown 107, both of which are integralwith stator 5, as well as the inner surface of stator 5. As is shown inthis figure, a portion 113 of fixed crown 107 extends into annularchannel 110 and the blades 2 sweep the annular channel on both sides ofprojection 113 of fixed crown 107. As the blades are rotated with therotor, they sweep the volume of the annular channel but have sufficientclearance so that they do not generate substantial friction when thedevice is empty.

The profile or fixed crown 107 can be circular, but is generallypreferred that it be helical whereby the distance of the face of fixedcrown 107 from the axis of the rotor is at a maximum on one side of thefeed hopper (which can be mounted on stator 5 but is not illustrated inthe drawing) and decreases in the direction of rotation to a minimum onthe other side of the feed hopper.

In accordance with this embodiment, the material to be extruded isdisplaced toward the center of the stator by the rotating blades and bythe fixed crown, the surface of which the blades approach as they rotatefrom the feed-hopper outlet toward the opposite side of the hopper. Ifdesired, the interior surfaces of the rotor and stator may be providedwith various relief elements such as blades, nozzles, screws, orpropellors or simply an axial protuberance depicted as 112 in thedrawmg.

FIG. 6 illustrates the position of the blades in the device shown inFIG. 5. It will be noted that the blades are arcuate and are disposed atan angle to impart a centripetal force to the material to be extruded.The top portion of fixed crown 107 with a helical profile and itsrelation to hopper 116 is more clearly illustrated in this figure.

It will be understood by those skilled in the art that the apparatus ofthis embodiment can similarly be adapted for use with an extruder havinga vertical axis.

In order to illustrate the effects and the advantages of an extruderaccording to the present invention, reference is made to the followingnonlimiting examples.

EXAMPLE I A vertical extruder of the type shown in FIG. 1 is formed of arotating plate having a diameter of 180 mm. The concentric annularchannel circumscribes this plate and has a horizontal or radial width ofmm. and a height in the direction of rotation of the rotor of 22 mm.adjacent the window of the hopper and 5 mm. on the opposite side of thehopper. The lower base of the channel is the inner stator surface andthe space between the plates is 5 mm. On the lower face of the rotorthere is located a cylindrical-shaped lug, the diameter of which isslightly less than the gap' between the plates. This lug lies in ahorizontal plane and is 32 mm. in length, of which 9.8

mm. extends into the annular channel. The rotor has a smooth surfaceexcept for this lug and an axial frustoconical crown of 20 mm.,' thebase of which is 60 mm. in diameter and which bears three blades. Thestator surface bears four blades, one end of each blade is located 86mm. from the center and the other one is located 62 mm. from thiscenter. A cylindrical die is located on the same axis as the rotor andhas a diameter of 8 mm.

. The extruder is provided with a hopper which feeds the annular cavitythrough a horizontal rectangular opening 40 mm. in length and 10 mm. inwidth.

I The extruder is started by rotating the rotor at a rate of 65 r.p.m.and the temperature is the gap between the plates is raised to 180 C. bymeans of the heating elements on the plates. Polyvinyl chloride, havinga viscosity number AFNOR of 80 (corresponding to a K value of 57stabilized by 2 parts of tin thioglycolate per 100 parts by weight ofpolymer, is introduced through the feed hopper. The resulting extrudedrod is formed at the rate of kg. per hour and is found to be irregularand having incompletely gelled zones.

EXAMPLE II The extruder utilized in Example I is utilized in thisexample, except that the rotor lug is replaced by three blades havingthe profile shown in FIG. 3. These blades have a length and a heightsuch that they sweep the gap between the planes and the annular channel.The blades are mounted upon a crown 136 mm. in diameter which is affixedto the surface of the rotor. The output of the apparatus using the sameresin as is used in Example I is 19.3 kg. per hour. It is noted thatfewer zones resulting from incomplete gelling are observed in the rod.

EXAMPLE III The extruder in Example 11 is used in this example, exceptthat the hopper is modified by closing the bottom and by providing aside opening having a width of 10 mm. and a height of 17 mm. on the sidefacing the direction of rotation of the rotor. it is found that atransparent rod of the resin utilized in Example I may be extrudedcontinuously and with increased regularity at a rate of 27.7 kg. perhour.

EXAMPLE IV An extruder of the type described in FIGS. 5 and 6 isprovided with a rotor having a diameter of 210 mm. and a gap dimensionof 6 mm. The axial dimension of the annular chanme]. is 23 mm. and thedistance from the face of the fixed crown to the machine axis rangesfrom 1 1.2 mm. on one side of the hopper to 9.9 mm. in the direction ofrotation at the other side of the hopper.

The internal surfaces of both the rotor and stator are each providedwith two blades which serve to sweep the gap therebetween. The axis ofthe rotor is provided with a nozzle without blades.

In the operation of this apparatus, the rotor is rotated ata rate of 65r.p.m. and the temperature of the plates is maintained at 180C. Thespace between the plates is fed with polyvinyl chloride powder havingviscosity number AFNOR of stabilized by 2.5 parts of tin thioglycolateper parts by weight of polymer.

The extrusion flow obtained is 60 kg. per hour, but is reduced to 25 kg.per hour by removing the blades from the rotor.

This example, in which no extrusion pressure is required since there isno die, demonstrates the difference in the feed capacities of bothsystems.

EXAMPLE V The operation of Example IV is repeated except that a rod diehaving a diameter of 4.5 mm. is added to the extruder, and is heated toC. The How of the extended rod when the rotor is provided with blades is28 kg. per hour as compared to 24 kg. per hour when the blades of therotor are removed.

This example illustrates that the use of an extruder having bladesprovides a pressure greater than that obtained without the use of suchblades.

EXAMPLE V] In this example, the extruder used in example V is usedexcept that the extruder nozzle was replaced by two blades. The flow ofthe extruded rod is 33 kg. per hour using blades on the rotor and 24 kg.per hour in the case of the apparatus without such blades.

It will be apparent from the foregoing that the present inventionprovides an improvement in the feed system of rotary plate extruders. Itwill be further apparent that the use of the invention results in feedcapacities which were hitherto unobtainable with prior art type rotaryplate extruders.

It will be understood that changes may be made in the details ofconstruction, arrangement, and operation without departing from thespirit of the invention, especially as defined in the following claims.

We claim:

1. In an extruder including a housing having a stator, a rotor mountedfor rotation in the form of a plate arranged in faceto-face relationwith said stator to define a gap between said rotor and said stator, anextrusion opening axially through said stator, and means for feedingmaterial to said extruder, the improvement comprising an annular channeldefined in said housing, said channel being outside the periphery ofsaid gap and communicating therewith, and deflector means mounted onsaid rotor and extending radially and outwardly therefrom to sweep thevolume of saidchannel.

2. An extrude as defined in claim 1 wherein said channel is bounded by asurface of said stator and by a helicoidal surface defined by a surfaceof said housing.

3. An extruder defined in claim 1 wherein said means for feedingmaterial to said extruder communicates with said channel;

4. An extruder as defined in claim 3 wherein said means for feedingmaterial to said extruder is at least one hopper, said hopper having aclosed bottom and having a window in one side thereof communicating withsaid channel.

5. An extrude as defined in claim 4 wherein said window lies in a planepassing through the axis of said rotor.

6. An extruder as defined in claim 5 wherein said channel is bounded bya helicoidal surface defined by the surface of said housing whereby themaximum height of said channel corresponds to the height of said windowplus the axial dimension of said gap and the minimum height of saidchannel corresponds to the axial dimension of said gap.

7. An extruder as defined in claim 1 wherein the axial dimension of saidchannel is the axial dimension of said gap.

8. An extruder as defined in claim 1 wherein the axial dimension of saidchannel adjacent said means for feeding said extruder is from 1 to 3times theaxial dimension of said gap andthe axial dimension of saidchannel on the other side of tending radially inwardly into saidchannel.

11. An extruder as defined in claim 11 wherein said crown has a helicalprofile 12. An extruder as defined in claim 1 wherein said means tosweep said channel comprises at least one blade mounted for rotation onsaid rotor.

Patent No. 3,602,943 Dated September 7, 197].

Inventor(s) Bernard Neuville, Claude Ledoux, Raoul Hess It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

column 1, line 29, change "whereby" to "thereby";

column 1, line 30, change "void" to "avoid" column 1, lines 32 and 44,omit the numeral "38" column 1, line 49, change "wherein" to "whereby"column 1, line 67, change "0" to "or" column 2, line 34, change "n" to"no" column 2, line 47, change "the" to "a" column 3, line 33, after"stator" insert "3" column 4, line 14, after "apparatus" insert"described in the foregoing figures without departing"I-.:-.

column 4, line 44, change "an" to "and" column 4, line 53, change "or"to "of" column 5, line 33, change "is" to "in" column 5, line 59, change"it" to "It" column 6, line 17, change "120" to "190"; same line,

change "extended" to "extruded" Claim 2, line 1, change "extrude" to"extruder" Signed and sealed this 21st day of March 1972 (SEAL) Attest:

EDWARD MmLETcHERQmRL] ROBERT GOTTSCHALK Attesting Officer Commis i ner fPatents RM po'mso USCOMM-DC wan-Poe U 5 GOVERNMENT PHINT'NG OFFICE L 19.DJ-l3

2. An extrude as defined in claim 1 wherein said channel is bounded by asurface of said stator and by a helicoidal surface defined by a surfaceof said housing.
 3. An extruder defined in claim 1 wherein said meansfor feeding material to said extruder communicates with said channel. 4.An extruder as defined in claim 3 wherein said means for feedingmaterial to said extruder is at least one hopper, said hopper having aclosed bottom and having a window in one side thereof communicating withsaid channel.
 5. An extrude as defined in claim 4 wherein said windowlies in a plane passing through the axis of said rotor.
 6. An extruderas defined in claim 5 wherein said channel is bounded by a helicoidalsurface defined by the surface of said housing whereby the maximumheight of said channel corresponds to the height of said window plus theaxial dimension of said gap and the minimum height of said channelcorresponds to the axial dimension of said gap.
 7. An extruder asdefined in claim 1 wherein the axial dimension of said channel is theaxial dimension of said gap.
 8. An extruder as defined in claim 1wherein the axial dimension of said channel adjacent said means forfeeding said extruder is from 1 to 3 times the axial dimension of saidgap and the axial dimension of said channel on the other side of saidmeans for feeding said extruder in the direction of rotation of saidrotor is equal to the axial dimension of said gap.
 9. An extruder asdefined in claim 1, wherein the radial dimension of said channel is 2 to5 times the axial dimension of said gap.
 10. An extruder as defined inclaim 1 wherein the periphery of said channel is bounded by the surfaceof a fixed crown extending radially inwardly into said channel.
 11. Anextruder as defined in claim 11 wherein said crown has a helical profile12. An extruder as defined in claim 1 wherein said means to sweep saidchannel comprises at least one blade mounted for rotation on said rotor.